Modified Bitumen Roofing: Everything You Need to Know

What is Modified Bitumen Roofing?

Modified bitumen roofing has been a reliable and popular type of commercial roofing in Virginia (and elsewhere) for decades. But what exactly is it? 

We like to think of modified bitumen as the next evolution of asphaltic roofing. Like other redundant roofing systems, modified bitumen roofing systems are made of multiple layers, more than single-ply roofs but fewer than other redundant roofing systems. 

Another redundant roofing system like Built-Up Roofing (or “BUR roofing”), for example, consists of five layers, including a weather layer (i.e flood coat and gravel, granule surfaced cap sheet, etc.). Here’s where modified bitumen’s superpower comes into play: they add plastic or rubber into their asphaltic mix, allowing the roof rolls/sheets to expand and contract more effectively. What that translates to is the same long warranty term with equal protection and fewer redundant layers…and of course fewer labor hours and less material equals lower cost of the project.  

That’s just the tip of the iceberg! Want to know more? Read on to learn anything and everything you’ve ever needed to know about modified bitumen roofing and how the best commercial roofing contractors tackle these projects.

What is Modified Bitumen material?

The biggest material difference in modified bitumen roofs is their additives (rubber or plastic) which gives it its unique abilities to move with the building (contraction/expansion) and adapt to changes in weather (hot/cold and freeze/thaw cycles).  

Modified membranes with a rubber additive are Styrene-butadiene-styrene or more commonly known as “SBS” whereas modified with a plastic additive is atactic polypropylene otherwise known as “APP”.  

These reinforced roofing rolls will include either a fiberglass mat or a polyester scrim, both of which have their own pros and cons but are generally seen as equals. Similarly, manufacturers will likely see them as equally eligible for 20 year warranties.

Modified Bitumen Roofs Have a Variety of Installation Methods

What most of our clients like and appreciate most about modified bitumen is its large variety of installation methods.

Other redundant roof types such as BUR roofing offer more restrictive options, usually limited to hot asphalt or cold applied installation options.

Modified bitumen roofing, on the other hand, can be installed in a variety of different ways, including hot asphalt applied, cold applied, torch applied, and self-adhered. Why is this advantageous? It means it’s more capable of accommodating a greater variety of building types and roof deckings.

If your building, for example, has a combustible deck type (i.e wood), we can easily avoid a more hazardous torch-applied method in favor of something safer. Likewise, for a more sensitive or conscious building type such as a hospital, it’s best to use the least hazardous or intrusive installation type, such as cold applied or self adhered.

Based on material, budget, or other factors, modified bitumen could very well be the ideal commercial roof type for you, and fortunately there’s an installation method that can accommodate just about any circumstance.

More Layers, More Protection

Like other redundant roof types, modified bitumen’s multiple layers of protection will lead to better waterproofing and durability. Compared to single ply roofs, modified bitumen roofs are less vulnerable to accidental punctures. 

Thanks to its versatility, modified bitumen is a great choice for just about every building type. Its durability makes it much more resilient to high foot traffic, so it’s an optimal choice for building types with a higher volume of roof-related maintenance or those with a lot of HVAC units or other hardware.

What’s the Catch?

It all seemed a little too good to be true, right? Well, quality comes at a price, and both its material and labor costs are considerably higher versus other roof types, especially single-ply roofs like TPO or PVC. TPO, by comparison, is far cheaper and provides similar lengths of warranty coverage to modified bitumen.  

It’s also significantly less customizable than single-ply roofs. All single-ply roofing systems benefit from a treasure trove of prefabricated accessories that make flashing detail and installation a breeze, allowing it to easily accommodate existing roof structures, obstructions, and units. 

Modified bitumen roofing, on the other hand, has little or no prefabricated accessories, making the installation process more demanding (and much harder to create pitch pockets or other roof details.) That’s why these complex commercial roofing installations are better suited for only the most qualified commercial roofing contractors. 

How About Repairs or Warranties?

The cost of commercial roof repairs always depends on the amount of material and number of required laborers. On the whole, repairs for modified bitumen are largely comparable to other roof types.

Assuming the building type is able to accommodate this installation method, Simpson Unlimited prefers torch-applied repairs. Why? These repairs create a strong bond over the new roof patch that cures almost immediately, whereas cold applied and self adhered options are temperature dependent.  

Warranties are also comparable to other major commercial roof types. Thanks to its long history in the field and record of success, manufacturer’s recognize it is a reliable, safe commercial roofing choice.

Quality comes at a price, and although it is a more expensive commercial roof system option compared to single-ply roofing system modified bitumen roofing is still considered one of the most durable, reliable, and go-to commercial roofing types on the market.

Think modified bitumen could be right for you? Give us a call to learn about our FREE commercial roof inspections and how we can provide the best commercial roofing contractor services in Virginia, Maryland, or DC!


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